Many photographic light-sensitive materials employ gelatin in layer as a binder, and gelatin can be hardened with various known compounds to ensure water resistance and mechanical strength of the gelatin layer.
Compounds known as gelatin hardeners include, for example, aldehyde compounds, e.g., formaldehyde, glutaraldehyde, etc.; compounds having a reactive halogen as described in U.S. Pat. No. 3,288,775; compounds having a reactive ethylenically unsaturated bond as described in U.S. Pat. No. 3,642,486 and Japanese Patent Publication No. 13563/74; aziridine compounds as described in U.S. Pat. No. 3,017,280; epoxy compounds as described in U.S. Pat. No. 3,091,537; halogencarboxylaldehydes, e.g., mucochloric acid, etc.; dioxanes, e.g., dihydroxydioxane, dichlorodioxane, etc.; and inorganic hardeners, e.g., chromium alum, zirconium sulfate, etc.
However, each of these known gelatin hardeners has one or more disadvantages, when used in photographic light-sensitive materials, such as (1) insufficient hardening effect, (2) long-term change in the degree of hardening, called after-hardening (arising from slow hardening reactivity), (3) adverse influences on photographic characteristics to cause, in particular, increase of fog and reduction of sensitivity, (4) loss of hardening effect due to other coexisting photographic additives, (5) adverse influences on other photographic additives, e.g., color couplers, to reduce their effects, and the like.
Hardeners exhibiting relatively high reaction rates on gelatin so as not to cause after-hardening have been proposed, including compounds having a dihydroquinoline skeleton as described in Japanese Patent Application (OPI) No. 38540/75 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"); compounds having a phosphorus-halogen bond as described in Japanese Patent Application (OPI) No. 113929/83; compounds having an N-sulfonyloxyimide group as described in Japanese Patent Application (OPI) No. 93470/77; compounds containing at least two N-acyloxyimino groups per molecule as described in Japanese Patent Publication No. 22089/78; N-carbamoylpyridinium salts as described in Japanese Patent Publication Nos. 12853/81 and 32699/83; 2-sulfonyloxypyridinium salts as described in Japanese Patent Application (OPI) No. 110762/81, etc.
These hardeners are characterized by their rapid hardening effects, causing less after-hardening. Inter alia, the hardeners described in Japanese Patent Publication No. 32699/83 exhibit excellent performances, such as a rapid hardening rate, good water-solubility which eliminates necessity of any special organic solvent on coating, freedom from a pyridine odor as compared with the compounds of Japanese Patent Publication No. 12853/81 (thus reducing the risk of harm to the health of workers), and the like.
Nevertheless, when the compounds of Japanese Patent Publication No. 32699/83 are used for hardening a gelatin layer of silver halide color photographic materials, they frequently suffer from inhibition of hardening, and fail to achieve sufficient hardening of the gelatin layer.
In general, silver halide color photographic materials comprise a support having provided thereon a plurality of gelatin layers, in some of which various photographically useful substances dissolved in high-boiling organic solvents are dispersed with the aid of surface active agents called emulsifiers, while exercising their respective intended functions. Among photographically useful substances are many compounds that are very apt to react with gelatin hardeners having high hardening reaction rates, typically exemplified by couplers. Therefore, when such a gelatin hardener that shows satisfactory performances in black-and-white photographic materials containing no high-boiling organic solvent is applied to color photographic materials, not only is sufficient hardening of photographic layers not assured, but also it often happens that the hardener reacts with, for example, a coupler, to seriously reduce maximum density of the resulting photographic image, or with an antifoggant to cause, on the contrary, a serious increase of a minimum density of the image, thus resulting in a considerable impairment of the commercial value of the materials. The causes of these phenomena have not yet been clearly elucidated, but it is believed that the gelatin hardener becomes incorporated into the aforesaid high-boiling organic solvent and undergoes chemical reaction with the photographically useful substance which is dispersed therein together with the organic solvent. Therefore, as the hardening rate of a gelatin hardener increases to show higher reactivity to a photographically useful substance, the above-described defect of hardening inhibition tends to become serious.
With the recent demand for reduction of development time of silver halide photographic materials, photographically useful substances to be employed therefor, e.g., couplers, tend to have so much increased reactivities. It is easily anticipated that the phenomenon of hardening inhibition would become more pronounced with this tendency. Therefore, a gelatin hardener which has a high hardening rate but is still free from hardening inhibition even when applied to silver halide color photographic materials has been keenly desired.